A characteristic feature of AB or ABA type block copolymers in solution is that they form sperical micelles in selective solvents which are thermodynamically good solvents for one block and poor solvents for the other. The free energy of the system is lowered in such solvents by micellar association compared to dispersed single chains. These micelles are made up of a compact core of the insoluble block with a soluble corona consisting of the second block. Since the association process is an equilibrium between micelles and free polymer (unimer), micellar stability can be influenced by the environment. Chemically fixing the core of the micelle could then render stability to the micellar aggregates.
It is known in the art to form a composition having a continuous organic phase having therein a copolymer micelle. The core is comprised of a less soluble or insoluble component of the block or graft copolymer and the shell or "corona" is formed of the organic solvent soluble component. It is also known to fix the insoluble core of the micelle by crosslinking. Reference is made to Park et al, Synthesis of Microphased Core-Corona Type Microgel, POLYMER COMMUNICATIONS, Vol 29 pg 230-231 (1988) and Ishizu and Fukutomi, Core-Shell Type Polymer Microspheres Prepared from Block Copolymers, J. Polymer Sci., Part C: Polymer Letters, Vol 26, 281-286 (1988). Such crosslinked micelles have not been isolated and no uses of the resulting particles are mentioned in these references.
No compositions are known of the general type described above where the continuous phase is water and the core of the micelle is a chemically fixed oleophilic component of the copolymer. That an oleophilic component can be identified, which is conveniently fixed in an aqueous medium, in the absence of surfactants, is not apparent.
It would be desirable to be able to form water based compositions since organic solvents often have adverse environmental impact. A further problem to be solved is to provide a composition that can carry in an aqueous medium, and possibly deliver in a controlled manner, hydrophobic materials such as photographically useful materials and biological agents.